from flask_wtf import FlaskForm
from wtforms.validators import ValidationError
import re


form_prefix_pattern = re.compile(r'(?<!^)(?=[A-Z])')


def LimitFileSize(max_size_mb):
    max_size_b = max_size_mb * 1024 * 1024
    def file_length_check(form, field):
        if len(field.data.read()) >= max_size_b:
            raise ValidationError(
                f'File size must be less or equal than {max_size_mb} MB'
            )
        field.data.seek(0)
    return file_length_check


class NopaqueForm(FlaskForm):
    def __init__(self, *args, **kwargs):
        if 'prefix' not in kwargs:
            kwargs['prefix'] = \
                form_prefix_pattern.sub('-', self.__class__.__name__).lower()
        super().__init__(*args, **kwargs)